Driving circuit and driving method for an electrophoretic display

ABSTRACT

A driving circuit for an electrophoretic display has a plurality of pixels ( 18 ) of an electrophoretic material which comprises charged particles ( 8, 9 ). The pixels ( 18 ) are associated with a respective first electrode ( 6 ) and second electrode ( 5, 5 ′) which present a drive voltage (VD) to the pixels ( 18 ) to at least enable the charged particles ( 8, 9 ) to occupy one of two limit positions between the first electrode ( 6 ) and the second electrode ( 5, 5 ′). The driving circuit comprises an addressing circuit ( 16, 10 ) which generates the drive voltage (VD) by applying between the first electrode ( 6 ) and the second electrode ( 5, 5 ′): (i) an reset pulse (RE) which has an energy content sufficient or larger than required for the charged particles ( 8, 9 ) to reach one of the limit positions, and (ii) a shaking pulse (SP 1 ) which at least partially overlaps the reset pulse (RE). The shaking pulse SP 1  has, during the reset pulse (RE), at least partially a level with an opposite polarity than a level of the reset pulse (RE). The shaking pulse (SPI) comprises at least one preset pulse (PR) having an energy sufficient to release the charged particles ( 8, 9 ) present in one of the limit positions, but insufficient to enable said particles ( 8, 9 ) to reach the other one of the limit positions.

The invention relates to an electrophoretic display, a driving circuitfor such an electrophoretic display, a display apparatus comprising suchan electrophoretic display, and a method of driving such anelectrophoretic display.

A display device of the type mentioned in the opening paragraph is knownfrom international patent application WO 99/53373. This patentapplication discloses an electronic ink display (also referred to asE-ink display) which comprises two substrates, one of which istransparent, the other substrate is provided with electrodes arranged inrows and columns. Display elements or pixels are associated withintersections of the row and column electrodes. Each display element iscoupled to the column electrode via a main electrode of a thin-filmtransistor (further referred to as TFT). A gate of the TFT is coupled tothe row electrode. This arrangement of display elements, TFT's and rowand column electrodes jointly forms an active matrix display device.

Each pixel comprises a pixel electrode which is the electrode of thepixel which is connected via the TFT to the column electrodes. During animage update period or image refresh period, a row driver is controlledto select all the rows of display elements one by one, and the columndriver is controlled to supply data signals in parallel to the selectedrow of display elements via the column electrodes and the TFT's. Thedata signals correspond to image data to be displayed.

Furthermore, an electronic ink is provided between the pixel electrodeand a common electrode provided on the transparent substrate. Theelectronic ink is thus sandwiched between the common electrode and thepixel electrodes. The electronic ink comprises multiple microcapsules ofabout 10 to 50 microns. Each microcapsule comprises positively chargedwhite particles and negatively charged black particles suspended in afluid. When a positive voltage is applied to the pixel electrode withrespect to the common electrode, the white particles move to the side ofthe microcapsule directed to the transparent substrate, and the displayelement appears white to a viewer. Simultaneously, the black particlesmove to the pixel electrode at the opposite side of the microcapsulewhere they are hidden from the viewer. By applying a negative voltage tothe pixel electrode with respect to the common electrode, the blackparticles move to the common electrode at the side of the microcapsuledirected to the transparent substrate, and the display element appearsdark to a viewer. When the electric field is removed, the display deviceremains in the acquired state and exhibits a bi-stable character. Thiselectronic ink display with its black and white particles isparticularly useful as an electronic book.

Grey scales can be created in the display device by controlling theamount of particles that move to the common electrode at the top of themicrocapsules. For example, the energy of the positive or negativeelectric field, defined as the product of field strength and time ofapplication, controls the amount of particles which move to the top ofthe microcapsules.

The known display device has the drawback that the appearance of a pixeldepends on the history of the voltages supplied across the pixel.

From the non-pre-published patent applications in accordance toapplicants docket referred to as PHNL020441 and PHNL030091 which havebeen filed as European patent applications 02077017.8 and 03100133.2 itis known to minimize the image retention by using preset pulses (alsoreferred to as the shaking pulse). Preferably, the shaking pulsecomprises a series of AC-pulses, however, the shaking pulse may comprisea single preset pulse only. The non-pre-published patent applicationsare directed to the use of shaking pulses, either directly before thedrive pulses, or directly before the reset pulse. A reset pulse has anenergy which is sufficient to bring the pixel into one of two limitoptical states. PHNL030091 further discloses that the picture qualitycan be improved by extending the duration of the reset pulse which isapplied before the drive pulse. The reset period now comprises a resetpulse and an over-reset pulse. This over-reset pulse, when added to thestandard reset pulse, results in an over-reset energy which is largerthan required to bring the pixel into one of two limit optical states.The duration of the over-reset pulse may depend on the requiredtransition of the optical state.

For example, if black and white particles are used, the two limitoptical states are black and white. In the limit state black, the blackparticles are at a position near to the transparent substrate, in thelimit state white, the white particles are at a position near to thetransparent substrate.

The drive pulse has an energy to change the optical state of the pixelto a desired level which may be in-between the two limit optical states.Also the duration of the drive pulse may depend on the requiredtransition of the optical state.

The non-prepublished patent application PHNL030091 discloses in anembodiment that the shaking pulse precedes the reset pulse. Each level(which is one preset pulse) of the shaking pulse has a durationsufficient to release particles present in one of the extreme positions,but insufficient to enable said particles to reach the other one of theextreme positions. The shaking pulse increases the mobility of theparticles such that the reset pulse has an immediate effect If theshaking pulse comprises more than one preset pulse, each preset pulsehas the duration of a level of the shaking pulse. For example, if theshaking pulse has successively a high level, a low level and a highlevel, this shaking pulse comprises three preset pulses. If the shakingpulse has a single level, only one preset pulse is present.

The driving of the electrophoretic display in accordance with thepresent invention differs from the driving disclosed in thenon-prepublished patent application PHNL030091 in that the shaking pulseoccurs at least partially during the reset pulse.

A first aspect of the invention provides a driving circuit for anelectrophoretic display as claimed in claim 1. A second aspect of theinvention provides a display apparatus as claimed in claim 11. A thirdaspect of the invention provides a method of driving an electrophoreticdisplay as claimed in claim 12. Advantageous embodiments of theinvention are defined in the dependent claims.

As discussed earlier, the shaking pulse may comprise a single presetpulse or a series of preset pulses. If the shaking pulse comprises asingle preset pulse this preset pulse occurs at least partially duringthe reset period. If the shaking pulse comprises several preset pulses,at least one of these preset pulses occurs at least partially during thereset period. If only one preset pulse is (partially) present during thereset period, this preset pulse needs to have a polarity which isopposite to the polarity of the reset pulse to have the shaking effect.If several preset pulses are present during the reset period, preferablythe polarity of the preset pulses alternates.

Because, in accordance with the first aspect of the invention, theshaking pulse occurs at least partially during the reset period, theimage update period becomes shorter, while still the image retention isdecreased. The image update period is the period of time required toupdate the optical state of all the pixels in accordance with an imageto be displayed. In today's electrophoretic displays, the image updateperiod lasts about a second. Usually, the image update period comprisessuccessively the shaking pulse, the reset pulse, and a drive pulse. Theimage update period may comprise further pulses. For example, furthershaking pulses may be present between the reset period and the drivepulse. A shorter image update period has the advantage that the userneeds to wait less if the image has to change, and that the display offast changing information becomes more practical. However, the use ofthis idea of overlapping at least part of the shaking pulse with thereset pulse is not limited to a fall image update period. It is alsobeneficial if the electrophoretic display has to be resetted only.

In an embodiment in accordance with the invention as claimed in claim 2,the reset period comprises both an over-reset pulse and a reset pulse,whereby the picture quality may be improved. If further is referred tothe reset pulse this may either refer to the reset pulse alone, or theover-reset pulse combined with the reset pulse.

In an embodiment in accordance with the invention as claimed in claim 3,the shaking pulse comprises several preset pulses. A first number of thepreset pulses occurs before the reset pulse and a second number of thepreset pulses occurs during the reset pulse. The advantage of stillhaving preset pulses preceding the reset pulse is to eliminate theeffect of dwell time so that the reset pulse takes effects immediatelyand the disturbance of reset can also be reduced.

In an embodiment in accordance with the invention as claimed in claim 4,all the preset pulses are generated during the reset pulse. Now, theduration of the image update period is minimal.

In an embodiment in accordance with the invention as claimed in claim 5,two successive preset pulses with a polarity opposite to the polarity ofthe reset pulse occur during the reset period separated by a separationperiod of time. The disturbance of the reset pulse is less than that thepreset pulses occur immediately adjacent with alternating polarity.

In an embodiment in accordance with the invention as claimed in claim 6,the preset pulses have a duration equal to the frame period. The frameperiod is the time required to select all the pixels of the display lineby line.

In an embodiment in accordance with the invention as claimed in claim 7,the duration of the preset pulses is longer than the frame period. Theselonger preset pulses further reduce the image retention, especially whenthe electrophoretic material has a strong dependence on the imagehistory and/or dwell time.

In an embodiment in accordance with the invention as claimed in claim 8,the shaking pulse which at least partially occurs during the reset pulseis applied during a usual image update period wherein the drive pulsesucceeds the reset pulse.

In an embodiment in accordance with the invention as claimed in claim 9,a further shaking pulse is present in-between the reset pulse and thedrive pulse. This has the advantage that the image retention decreases.

In an embodiment in accordance with the invention as claimed in claim10, the preset pulses of the at least partially overlapping shakingpulse have a duration which is longer than a duration of the presetpulses of the shaking pulse which is present in-between the reset pulseand the drive pulse. These longer preset pulses further reduce the imageretention, especially when the electrophoretic material has a strongdependence on the image history and/or dwell time.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows diagrammatically a cross-section of a portion of anelectrophoretic display,

FIG. 2 shows diagrammatically a picture display apparatus with anequivalent circuit diagram of a portion of the electrophoretic display,

FIG. 3 shows voltages across a pixel in different situations wherein areset pulse and various shaking pulses are used,

FIG. 4 shows an embodiment in accordance with the invention wherein theshaking pulse partially overlaps the reset pulse,

FIG. 5 shows embodiments in accordance with the invention wherein theshaking pulse occurs during the reset pulse, and

FIG. 6 shows signals occurring during a frame period.

FIG. 1 shows diagrammatically a cross-section of a portion of anelectrophoretic display, for example, only of the size of a few displayelements, comprising a base substrate 2, an electrophoretic film with anelectronic ink which is present between two transparent substrates 3 and4 which, for example, are of polyethylene. One of the substrates 3 isprovided with transparent pixel electrodes 5, 5′ and the other substrate4 with a transparent counter electrode 6. The electronic ink comprisesmultiple microcapsules 7 of about 10 to 50 microns. Each microcapsule 7comprises positively charged white particles 8 and negatively chargedblack particles 9 suspended in a fluid 40. The dashed material 41 is apolymer binder. The layer 3 is not necessary, or could be a glue layer.When the pixel voltage VD across the pixel 18 (see FIG. 2) is suppliedas a positive drive voltage Vdr (see, for example, FIG. 3) to the pixelelectrodes 5, 5′ with respect to the counter electrode 6, an electricfield is generated which moves the white particles 8 to the side of themicrocapsule 7 directed to the counter electrode 6 and the displayelement will appear white to a viewer. Simultaneously, the blackparticles 9 move to the opposite side of the microcapsule 7 where theyare hidden from the viewer. By applying a negative drive voltage Vdrbetween the pixel electrodes 5, 5′ and the counter electrode 6, theblack particles 9 move to the side of the microcapsule 7 directed to thecounter electrode 6, and the display element will appear dark to aviewer (not shown). When the electric field is removed, the particles 8,9 remain in the acquired state and the display exhibits a bi-stablecharacter and consumes substantially no power. Electrophoretic media areknown per se from e.g. U.S. Pat., No. 5,961,804, U.S. Pat. No.6,1120,839 and U.S. Pat. No. 6,130,774 and may be obtained from E-inkCorporation.

FIG. 2 shows diagrammatically a picture display apparatus with anequivalent circuit diagram of a portion of the electrophoretic display.The picture display device I comprises an electrophoretic film laminatedon the base substrate 2 provided with active switching elements 19, arow driver 16 and a column driver 10. Preferably, the counter electrode6 is provided on the film comprising the encapsulated electrophoreticink, but, the counter electrode 6 could be alternatively provided on abase substrate if a display operates based on using in-plane electricfields. The counter electrode 6 may be segmented. Usually, the activeswitching elements 19 are thin-film transistors TFT. The display device1 comprises a matrix of display elements associated with intersectionsof row or selection electrodes 17 and column or data electrodes 11. Therow driver 16 consecutively selects the row electrodes 17, while thecolumn driver 10 provides data signals in parallel to the columnelectrodes 11 for the selected row electrode 17. Preferably, a processor15 firstly processes incoming data 13 into the data signals to besupplied by the column electrodes 11.

The drive lines 12 carry signals which control the mutualsynchronisation between the column driver 10 and the row driver 16.

The row driver 16 supplies an appropriate select pulse to the gates ofthe TFT's 19 which are connected to the particular row electrode 17 toobtain a low impedance main current path of the associated TFT's 19. Thegates of the TFT's 19 which are connected to the other row electrodes 17receive voltages such that their main current paths have a highimpedance. The low impedance between the source electrodes 21 and thedrain electrodes of the TFT's allows the data voltages present at thecolumn electrodes 11 to be supplied to the drain electrodes which areconnected to the pixel electrodes 22 of the pixels 18. In this manner, adata signal present at the column electrode 11 is transferred to thepixel electrode 22 of the pixel or display element 18 coupled to thedrain electrode of the TFT if the TFT is selected by an appropriatelevel on its gate. In the embodiment shown, the display device of FIG. 1also comprises an additional capacitor 23 at the location of eachdisplay element 18. This additional capacitor 23 is connected betweenthe pixel electrode 22 and one or more storage capacitor lines 24.Instead of TFTs, other switching elements can be used, such as diodes,MIMs, etc.

FIG. 3 shows voltages across a pixel in different situations wherein areset pulse is used. By way of example, FIGS. 3 are based on anelectrophoretic display with black and white particles and four opticalstates: black B, dark grey G1, light grey G2, white W. FIG. 3A shows animage update period IUP for a transition from light grey G2 or white Wto dark grey G0. FIG. 3B shows an image update period IUP for atransition from dark grey GI or black B to dark grey G1. The verticaldotted lines represent the frame periods TF (which usually last 20milliseconds), the line periods TL occurring within the frame periods TFare not shown in FIGS. 3 to 5. The line periods TL are illustrated inFIG. 6.

In both FIG. 3A and FIG. 3B, the pixel voltage VD across a pixel 18comprises successively first shaking pulses SP1, SP1′, a reset pulse RE,RE′, second shaking pulses SP2, SP2′ and a drive pulse Vdr. The drivepulses Vdr occur during the same drive period Tdr which lasts frominstant t7 to instant t8. The second shaking pulses SP2, SP2′immediately precede the driving pulses Vdr and thus occur during a samesecond shaking period TS2. The reset pulse RE, RE′ immediately precedethe second shaking pulses SP2, SP2′. However, due to the differentduration TR1, TR1′ of the reset pulses RE, RE′, respectively, thestarting instants t3 and t5 of the reset pulses RE, RE′ are different.The first shaking pulses SP1, SP1′ which immediately precede the resetpulses RE, RE′, respectively, thus occur during different first shakingperiods in time TS1, TS1′, respectively.

The second shaking pulses SP2, SP2′ occur for every pixel 18 during asame second shaking period TS2. This enables to select the duration ofthis second shaking period TS2 much shorter as is shown in FIGS. 3A and3B. For clarity, each one of levels of the second shaking pulses SP2,SP2′ is present during a standard frame period TF. In fact, during thesecond shaking period TS2, the same voltage levels can be supplied toall the pixels 18. Thus, instead of selecting the pixels 18 line byline, it is now possible to select all the pixels 18 at once, and only asingle line select period TL (see FIG. 6) suffices per level. Thus, inthe embodiment in accordance with the invention shown in FIGS. 3A and3B, the second shaking period TS2 only needs to last four line periodsTL instead of four standard frame periods TF. It is still possible toselect all the pixels during a longer period than a single line periodto decrease the power consumption. It is also possible to selectsuccessively groups of rows of pixels to lower the capacitive currentsrequired to charge the pixels.

Alternatively, it is also possible to change the timing of the drivesignals such that the first shaking pulses SP1 and SP1′ are aligned intime, the second shaking pulses SP2 are then no longer aligned in time(not shown). Now the duration of the first shaking period TS1 can bemuch shorter or it is possible to decrease the power consumption.

The driving pulses Vdr are shown to have a constant duration, however,the drive pulses Vdr may have a variable duration.

If the drive method shown in FIGS. 3A and 3B is applied to theelectrophoretic display, outside the second shaking period TS2, thepixels 18 have to be selected line by line by activating the switches 19line by line. The voltages VD across the pixels 18 of the selected lineare supplied via the column electrodes 11 in accordance with the opticalstate the pixel 18 should have. For example, for a pixel 18 in aselected row of which pixel the optical state has to change from white Wto dark grey G1, a positive voltage has to be supplied at the associatedcolumn electrode 11 during the frame period TF starting at instant t0.For a pixel 18 in the selected row of which pixel the optical state hasto change from black B to dark grey G1, a zero voltage has to besupplied at the associated column electrode during the frame period TFlasting from instants t0 to t1.

FIG. 3C shows a waveform which is based on the waveform shown in FIG.3B. This waveform of FIG. 3C causes the same optical transition. Thedifference is that the first shaking pulses SP1′ of FIG. 3B are nowshifted in time to coincide with the shaking pulses SP1 of FIG. 3A. Theshifted shaking pulses SP1′ are indicated by SP1″. Thus, now,independent on the duration of the reset pulse RE, also all the shakingpulses SP1, SP1″ occur during the same shaking period TS1. This has theadvantage that independent of the optical transition, the same shakingpulses SP1, SP1″ and SP2, SP2′ can be supplied to all pixels 18simultaneously. Thus both during the first shaking period TS1 and thesecond shaking period TS2, it is not required to select the pixels 18line by line. Whilst in FIG. 3C the shaking pulses SP1″ and SP2′ have apredetermined high or low level during a complete frame period, it ispossible to use shaking pulses SP1″ and SP2′ lasting one or more lineperiods TL (see FIG. 6). In this manner, the image update time may beshortened. Further, due to the selection of all (or groups of) lines atthe same time and providing a same voltage to all columns, during theshaking periods TS1 and TS2, the parasitic capacitances betweenneighboring pixels and electrodes will have no effect This will minimizestray capacitive currents and thus dissipation. Even further, the commonshaking pulses Sp1, Sp1″ and SP2, SP2′ enable implementing shaking byusing structured counter electrodes 6. The dissipation will be loweredif a same shaking pulse is supplied to all pixels 18 of the same column,wherein different columns may receive different shaking pulses.

A disadvantage of this approach is that a small dwell time is introduced(between the first shaking pulse period TS1 and the reset period TR1′).Dependent on the electrophoretic display used, this dwell time shouldnot become longer than, for example, 0.5 seconds.

FIG. 3D shows a waveform which is based on the waveform shown in FIG.3C. To this waveform third shaking pulses SP3 are added which occurduring a third shaking period TS3. The third shaking period TS3 occursbetween the first shaking pulses Sp1 and the reset pulse RE′, if thisreset pulse RE′ does not have its maximum length. The third shakingpulses SP3 may have a lower energy content than the first shaking pulsesSp1 to minimize the visibility of the shaking. It is also possible thatthe third shaking pulses SP3 are a continuation of the first shakingpulses SP1. Preferably, the third shaking pulses SP3 fill up thecomplete period in time available between the first shaking period TS1′and the reset period TR1′ to minimize the image retention and toincrease the grey scale accuracy. With respect to the embodiment inaccordance with the invention shown in FIG. 3C, the image retention isfurther reduced and the dwell time is massively reduced.

Alternatively, it is possible that the reset pulse RE′ occursimmediately after the first shaking pulses SP1 and the third shakingpulses occur between the reset pulse RE′ and the second shaking pulsesSP2′.

The shaking pulses which at least partially overlap the reset pulse inaccordance with the invention may be applied to any of the situationsshown in one of the FIGS. 3A to 3D. It is even possible to apply theinvention to a drive cycle of the electrophoretic display which is notan image update cycle but, for example a reset cycle only.

Several embodiments in accordance with the invention of shaking pulseswhich partially overlap the reset pulse are shown in FIGS. 4 and 5.

FIG. 4 shows an embodiment in accordance with the invention wherein theshaking pulse partially overlaps the reset pulse. FIG. 4A is identicalto FIG. 3A and is thus not further elucidated. For the opticaltransition from white W to dark grey GI the reset pulse RE needs to havethe duration TR1 shown in FIG. 4A. For other optical transitions thereset pulse RE may have a different duration. FIG. 4B shows that, forthe same optical transition, the first shaking pulse SP1 partly overlapsthe reset pulse RE. Or said in other words, the staring part of thereset pulse RE is replaced by the last part of the first shaking pulseSp1. In this example, the shaking pulse Sp1 comprises 6 preset pulsesPR1 to PR6 which alternate in polarity. The first preset pulse PR1 hasthe same polarity as the reset pulse RE. The first and the second presetpulses or levels PR1 and PR2 occur before the start of the reset pulseRE. The other 4 preset pulses PR3 to PR6 occur during the reset pulseRE. Consequently, the image update time IUP decreased to IUP′. In thisexample, the new image update time IUP′ is four times the duration ofone preset pulse PR shorter than the original image update time IUP. Theduration of one preset pulse PR is usually equal to one frame period TF.

FIG. 4C shows that, for the same optical transition, the first shakingpulse Sp1 partly overlaps the reset pulse RE. Or said in other words,the starting part of the reset pulse RE is replaced by the last part ofthe first shaking pulse Sp1. In this example, the shaking pulse Sp1comprises 6 preset pulses PR: the first preset pulse PR1 has the samepolarity as the reset pulse RE. The first and the second preset pulsesPR1 and PR2 occur before the start of the reset pulse RE. The otherpreset pulses PR4 and PR6 occur during the reset pulse RE. The durationof the preset pulses PR3 and PR5 which have the same polarity as thereset pulse RE have a longer duration than the preset pulse PR2, PR4 andPR6 which have the opposite polarity. Consequently, the image updatetime IUP decreased to IUP′. In this example, the new image update timeIUP′ is four times the duration of one preset pulse PR shorter than theoriginal image update time IUP. The duration of one preset pulse PR isusually equal to one frame period TF.

FIG. 5 shows embodiments in accordance with the invention wherein theshaking pulse occurs during the reset pulse.

FIG. 5A shows an example of preset pulses PR occurring completely duringthe reset period RE. In this example, three preset pulses PR with apolarity opposite to the polarity of the reset pulse RE are present.Successive preset pulses PR are separated by a separation time periodTSE which has a duration longer than the duration of the preset pulsesPR. As now the complete shaking pulse Sp1 occurs during the reset pulseRE, the minimal possible image update period IUP″ is reached for thisparticular optical transition. This image update period IUP″ is onlydetermined by the duration of the reset pulse RE required for theparticular optical transition and the duration of other pulses, ifpresent. If a reset-only cycle is performed, no other pulses arepresent. If an image update cycle is performed, at least a drive pulseVdr will be present. It is also possible that a further shaking pulseSP2 is present inbetween the reset pulse RE and the drive pulse Vdr, asis shown in FIG. 5A. Thus in fact, the reset pulse RE has still theoriginal duration TR1 but is interrupted by the preset pulses PR.

FIG. 5B differs from FIG. 5A in that, during the reset pulse RE morepreset pulses PR are present. Because the preset pulses PR are presentduring the reset pulse RE it is possible to increase the number ofpreset pulses PR to further decrease the image retention withoutincreasing the duration of the image update period IUP″. Again, it ispossible to have two successive preset pulses PR separated by aseparation time period TSE′ which has a duration longer than theduration of the preset pulses PR FIG. 5C differs from FIG. 5A in thatthe duration of the preset pulses is two frames instead of one frame.This has the advantage that these prolonged AC-pulses reduce the imageretention, especially when the electrophoretic material (for example theE-ink) has a strong dependence on the image history and/or dwell time.It is not essential to this embodiment in accordance with the inventionthat duration of the preset pulses PR is exactly two frame periods TF,any duration longer than one frame period TF will reduce the imageretention and improve the image quality.

FIG. 6 shows signals occurring during a frame period. Usually, eachframe period TF indicated in FIGS. 3 to 5 comprises a number of lineperiods TL which is equal to a number of rows of the electrophoreticmatrix display. In FIG. 6, one of the successive frame periods TF isshown in more detail. This frame period TF starts at the instant t10 andlasts until instant t14. The frame period TF comprises n line periodsTL. The first line period TL lasts from instant t10 to t11, the secondline period TL lasts from instant t11 to t12, and the last line periodTL lasts from instant t13 to t14.

Usually, during the frame period TF, the rows are selected one by one bysupplying appropriate select pulses SE1 to SEn to the rows. A row may beselected by supplying a pulse with a predetermined non-zero level, theother rows receive a zero voltage and thus are not selected. The data DAis supplied in parallel to all the pixels 18 of the selected row. Thelevel of the data signal DA for a particular pixel 18 depends on theoptical state transition of this particular pixel 18.

Thus, if different data signals DA may have to be supplied to differentpixels of a selected row, the frame periods TF shown in FIGS. 3 to 5comprise the n line or select periods TL. However, if the first andsecond shaking pulses Sp1 and SP2 occur during the same shaking periodsTS1 and TS2, respectively, for all the pixels 18 simultaneously, it ispossible to select all the lines of pixels 18 simultaneously and it isnot required to select the pixels 18 line by line. Thus, during theframe periods TF shown in FIGS. 3 and 6 wherein common shaking pulsesare used, it is possible to select all the pixels 18 in a single lineperiod TL by providing the appropriate select pulse to all the rows ofthe display. Consequently, these frame periods may have a significantlyshorter duration (one line period TL, or a number of line periods lessthan n, instead of n) than the frame periods wherein the pixels 18 mayreceive different data signals.

By way of example, the addressing of the display is elucidated in moredetail with respect to FIG. 3C. At the instant t0 a first frame periodTF of an image update period IUP starts. The image update period ends atthe instant t8.

The first shaking pulses SP1′ are supplied to all the pixels 18 duringthe first shaking period TS1 which lasts from instant t0 to instant t3.During this first shaking period TS1, during each frame period TF, allthe lines of pixels 18 are selected simultaneously during at least oneline period TL and the same data signals are supplied to all columns ofthe display. The level of the data signal is shown in FIG. 3C. Forexample, during the first frame period TF lasting from instant t0 to t1,a high level is supplied to all the pixels. During the next frame periodTF starting at instant t1, a low level is supplied to all the pixels. Asame reasoning is valid for the common second shaking period TS2.

The duration of the reset pulse RE, RE′ may be different for differentpixels 18 because the optical transition of different pixels 18 dependson the image displayed during a previous image update period IUP and theimage which should be displayed at the end of the present image updateperiod IUP. For example, a pixel 18 of which the optical state has tochange from white W to dark grey G1, a high level data signal DA has tobe supplied during the frame period TF which starts at instant t3, whilefor a pixel 18 of which the optical state has to change from black B todark grey G1, a zero level data signal DA is required during this frameperiod. The first non-zero data signal DA to be supplied to this lastmentioned pixel 18 occurs in the frame period TF which starts at theinstant t4. In the frames TF wherein different data signals DA may haveto be supplied to different pixels 18, the pixels 18 have to be selectedrow by row.

Thus, although all the frame periods TF in FIGS. 3 to 5 are indicated byequidistant vertical dotted lines, the actual duration of the frameperiods may be different. In frame periods TF in which different datasignals DA have to be supplied to the pixels 18, usually the pixels 18have to be selected row by row and thus n line select periods TL arepresent. In frame periods TF in which the same data signals DA have tobe supplied to all the pixels 18, the frame period TF may be as short asa single line select period TL. However, it is possible to select allthe lines simultaneously during more than a single line select period TLto decrease the power consumption. It is possible to select all thelines (or a group of lines) at the same time if the signals to besupplied to each one of the columns are the same for all pixels of oneof the columns, the signals supplied to different columns may differ.

The implementation of the embodiments in accordance with the inventionas illustrated in FIGS. 4 and 5 in the picture display apparatus shownin FIG. 2 is straightforward to the skilled person and therefore notexplained in detail. The control of the row driver 16 and the columndriver 10 by the processor 15 is adapted such that the desired voltagelevel is applied between the pixel electrodes 5, 5′ and the counterelectrode 6 as shown in FIGS. 4 to 5. Thus, with respect to the knowndisplay apparatus, only the timing of when which level has to be appliedto which pixel 18 has been changed to obtain the waveforms shown.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. For example, the second shaking pulsesSP2 need not be present. Although in the figures, is referred to shakingpulses, each of which comprises several levels or preset pulses, it ispossible that the shaking pulses comprise a single level or preset pulseonly.

The present invention is also applicable to voltage modulation drivingwherein the levels of the shaking pulses, the reset pulses and the drivepulses may vary.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means maybe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

1. A driving circuit for an electrophoretic display with a plurality ofpixels (18) having an electrophoretic material comprising chargedparticles (8, 9), the pixels (18) being associated with a respectivefirst electrode (6) and second electrode (5, 5′) for presenting drivevoltage waveforms (VD) across the pixels (18) for at least enabling thecharged particles (8, 9) to occupy one of two limit positions betweenthe first electrode (6) and the second electrode (5, 5′), the drivingcircuit comprising an addressing circuit (16, 10) for generating thedrive voltage waveforms (VD) comprising: (i) a reset period comprising areset pulse (RE) having an energy content being sufficient for thecharged particles (8, 9) to reach one of the limit positions, and (ii) ashaking pulse (SP1) occurring at least partially during the reset pulse(RE), and having during the reset pulse (RE) at least partially a levelwith an opposite polarity than a level of the reset pulse (RE), theshaking pulse (SP1) comprising at least one preset pulse (PR) having anenergy sufficient to release the charged particles (8, 9) present in oneof the limit positions but insufficient to enable said particles (8, 9)to reach the other one of the limit positions.
 2. A driving circuit foran electrophoretic display as claimed in claim 1, wherein the addressingcircuit (16, 10) is arranged for generating the reset period furthercomprising an over-reset pulse, which when added to the reset pulse,results in an over-reset energy which is larger than required to bringthe pixel into one of two limit optical states.
 3. A driving circuit foran electrophoretic display as claimed in claim 1, wherein the addressingcircuit (16, 10) is arranged for generating the shaking pulse (SP1)having a first predetermined number (N1) of preset pulses (PR) occurringbefore a start of the reset pulse (RE) and a second predetermined number(N2) of preset pulses (PR) during the reset pulse (RE).
 4. A drivingcircuit for an electrophoretic display as claimed in claim 1, whereinthe addressing circuit (16, 10) is arranged for applying all the presetpulses of the shaking pulse (SP) during the reset pulse (RE) tointerrupt the reset pulse during the at least one preset pulse (PR). 5.A driving circuit for an electrophoretic display as claimed in claim 1,wherein the addressing circuit (16, 10) is arranged for generatingduring the reset pulse (RE) at least two preset pulses (PR) with apolarity opposite to the polarity of the reset pulse (RE), the twopreset pulses (PR) being separated from each other by a separation timeperiod (TSE) lasting longer than a duration of the preset pulses (PR).6. A driving circuit for an electrophoretic display as claimed in claim1, wherein the addressing circuit (16, 10) is arranged for generatingthe at least one preset pulse (PR) having a duration substantially equalto a frame period (TF) during which all lines of pixels (18) areaddressed one by one.
 7. A driving circuit for an electrophoreticdisplay as claimed in claim 1, wherein the addressing circuit (16, 10)is arranged for generating the at least one preset pulse (PR) having aduration substantially longer than a frame period (TF) during which alllines of pixels (18) are addressed one by one.
 8. A driving circuit foran electrophoretic display as claimed in claim 1, wherein the addressingcircuit (16, 10) is arranged for further generating a drive pulse (Vdr)having a energy content in accordance with an optical state to bereached by the associated one of the pixels (18) to display apredetermined image, the drive pulse (Vdr) occurring after the resetpulse (RE).
 9. A driving circuit for an electrophoretic display asclaimed in claim 7, wherein the addressing circuit (16, 10) is arrangedfor further generating a further shaking pulse (SP2) in-between thereset pulse (RE) and the drive pulse (Vdr).
 10. An electrophoreticdisplay as claimed in claim 8, wherein the addressing circuit (16,10) isarranged for further generating the first mentioned shaking pulse (SP1)comprising the at least one first mentioned preset pulse (PR) having afirst duration, and the further shaking pulse (SP2) comprising at leastone further preset pulse (PR′) having a second duration being shorterthan the first duration.
 11. A display apparatus comprising anelectrophoretic display with a plurality of pixels (18) having anelectrophoretic material (8, 9) comprising charged particles, each oneof the pixels (18) being associated with a respective first electrode(6) and second electrode (5, 5′) for presenting a drive voltage (VD)across each one of the pixels (18) for at least enabling the chargedparticles to occupy one of two limit positions between the firstelectrode (6) and the second electrode (5, 5,), and a driving circuit asclaimed in claim
 1. 12. A method of driving an electrophoretic displaywith a plurality of pixels (18) having an electrophoretic material (8,9) comprising charged particles, the pixels (18) being associated with arespective first electrode (6) and second electrode (5) for presenting adrive voltage (VD) across the pixels (18) to at least enable the chargedparticles to occupy one of two limit positions between the firstelectrode (6) and the second electrode (5), t he method of drivingcomprising addressing (16, 10) for generating the drive voltage (VD) byapplying between the first electrode (6) and the second electrode (5):(i) an reset pulse (RE) having an energy content being larger thanrequired for the charged particles to reach one of the limit positions,and (ii) a shaking pulse (Sp1) occurring at least partially during thereset pulse (RE), and having during the reset pulse (RE) at leastpartially a level with an opposite polarity than a level of the resetpulse (RE), the shaking pulse (Sp1) comprising at least one preset pulse(PR) having an energy sufficient to release the charged particles (8, 9)present in one of the limit positions but insufficient to enable saidparticles (8, 9) to reach the other one of the limit positions.